Chemical sensitization of photographic emulsions



United States Patent CHEMICAL SENSITIZATION OF PHOTOGRAPHIC EMULSIONSWesley G. Lowe, Jean E. Jones, and Harry E. Roberts,

Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y.,a corporation of New Jersey No Drawing. Application November 8, 1952,Serial No. 319,618

1 Claim. (Cl. 95-7) from the reduction of silver halide, which effectmay be in addition to the former effect usually known as sulfursensitizing. The present invention is concerned primarily with chemicalsensitization apparently of the latter type.

It has been proposed to use organic and inorganic sulfides in'photographic emulsions to increase thesensitivity thereof. The compoundsare generally regarded as imparting the above-mentioned type of sulfursensitizing resulting from the formation of silver sulfide nuclei on thesilver halide grains. In the Lowe et al. U. S. Patent 2,521,926 grantedSeptember 12, 1950, have been proposed a group of organicsulfur-containing compounds which have little or no activity as sulfursensitizing agents but which appear to depend for their sensitizingeffect upon enlargement of the silver sulfide nuclei by deposition ofsilver thereon through reduction of silver halide. Whatever themechanism involved, the sensitizing eflect is readily distinguishablefrom ordinary sulfur sensitizing and when employed in conjunction withsulfur sensitizing can be separately evaluated.

We have now found that when silver halide emulsions are sensitized witha mixture of a sulfur sensitizing agent, a gold salt sensitizing agentand the organic sulfide sensitizing agents of the Lowe et a1. invention,a speed increase is obtained greater than that expected from theindividual effects of the sensitizing agents and greater than thatexpected from the combined effect of any two of the three types ofsensitizing agents.

Therefore, one object of our invention is to provide chemicallysensitized emulsions of enhanced light sensitivity. Another object is toprovide emulsions having sensitivity enhanced by the combined efiect ofsulfur, gold and certain organic sulfide compounds. A further object isto provide the methods of augmenting emulsion sensitivity utilizing thenovel combination of sensitizing agents. Another object is to providephotographic elements in which the novel emulsions are useful. Furtherobjects of our invention will become apparent from consideration of thefollowing description.

The objects of our invention are accomplished by the incorporation intosilver halide emulsions of a mixture of' (A) a sulfur-sensitizing agentsuch as disclosed in Sheppard U. S. Patents 1,574,944 granted March 2,1926, and 1,623,499 granted April 5, 1927, e. g. thiourea, di-o-tolylthiourea, allyl isothiocyanate, thiocarbanilide, sodium thiosulfate,thioacetamide and allyl thiourea, (B) a gold salt sensitizing agent suchas disclosed in Waller 2 t and Dodd U. S. Patent 2,399,083 e. g. goldchloride, potassium chloroaurate or an alkali metal aurothiocyanate suchas potassium aurothiocyanate, and (C) either bis- (fi-aminoethyl)sulfide (NHzCH2CH2)2S and its watersoluble salts obtained fromnon-desensitizing acids such as the acetates, carbonates, sulfates andhydrochloride salts, or bis-(y-diethyl aminopropyl) disulfide at anystage in their preparation but preferably before digestion is complete.

The quantity of sulfur, gold and organic sulfide sensitizing agents usedin the emulsions is not especially critical and can be varied from theoptimum amounts indicated in the following examples.

The sensitizing agents are incorporated into the emulsions at any stagein their preparation but, preferably before digestion is complete. Thatis, the emulson can first be sensitized with a sulfur sensitizing agentand a gold salt sensitizing agent and then one of the organic sulfidesensitizing agents indicated, or the addition of the organic sulfidecompound can be made prior to the'addition of p the gold saltsensitizing compound. However, it is preferred to partially digest theemulsion in the presence of the selected sulfur and gold sensitizingagents and to finish the emulsion by digesting it further after additionof the organic sulfide compound since the greatest One rather speedincreases are obtained in this manner. unexpected feature of ourinvention resides in the fact that while the emulsions can be digestedto optimum sensitivity in the presence of the sulfur and goldsensitizing agents, further digestion after addition of the organicsulfide compound does not cause any appreciable increase in fog.

The following examples illustrateirneans for carrying out our invention:7

Example 1 p A. In a positive type of silver bromoiodide emulsion wereincorporated 20 milligrams of allyl thiourea per mol of silver halideand 2 milligrams of potassium chloro aurate per mol of silver halide andthe emulsion was digested for 61 minutes at 62 C. A sample of theemulsion was coated onto film base. i

B. To a sample of emulsion A above were added 400 milligrams ofbis-(,B-aminoethyl) sulfide dihydrochloride per mol of silver halide andthe emulsion was digested for 20 minutes at 40 C. before coating on filmbase.

C. An emulsion was prepared as in B except using 600 milligrams of thesulfide per mol of silver'halide.

The coatings of emulsions A, B and C were exposed in the sensitometerand developed for 3 minutes in the following developer:

Water, about F. (50 C.) cc 500 p-Methylamino-phenol sulfate grams 2.2Sodium sulfite, desiccated do 96.0 Hydroquinone do 8.8 Sodium carbonate,desiccated do 48.0 Potassium bromide ..do 5.0 Cold water to make 1.0liter.

Example 2 D. To a fine-grained gelatino silver bromoiodide emulsion wereadded a sulfur sensitizer such as described above and a gold saltsensitizer such as described above. The emulsion was then digested to.optimum sensitivity and a sample coated on film.

E. A portion of the digested emulsion of D was treated, with 0.400 gramof bis-(p-aminoethyl) sulfide per mol of silver halide and the emulsionwas held at 40 C. for 30 minutes, then coated on to film.

F. A portion of the digested emulsion of D was treated with 0.800 gramof bis-(fl-aminoethyl) sulfide per mol Patented Mar. 20, 1956 uf silverhalide and the emulsion was held at 40 C. for 30 minutes, then coated onto film.

The coated films of emulsions D, E and F were then exposed in an Eastmantype lb sensitometer and processed for 5 minutes in a developer of thefollowing composition:

Water liters l p-Methylaminophenol sulfate grams 0 3 Hydroquinone do 6.0Sodium sulfite (dry) do 38.0 Sodium bisulfite do 1.2 Sodium carbonate(dry) do 19.0 Potassium bromide do 0.9 Citric acid do 0.7

The sensitometric characteristics of the coatings of Examples 1 and 2are tabulated in the following table:

Sample Sensitizer spew Gamma Fo A Suliur+gold 5. 4 3. 28 0. 04 B---Sulfur+gold+sulfide 8.6 3. 48 0. 04 0. do 9.4 3. 50 004 D. Sulfur+gold37 2. 27 0. 02 SulIur+gold+su1fide 43 2. 51 0. 03 ""410 46 2. 47 0.03

silver halide emulsions can be treated with the novel combination ofsulfur, gold and organic sulfide sensitizing agents. The novelsensitizers may, in general, be employed in hydrophilic colloid emulsionvehicles; for example, gelatin, polyvinyl alcohol, partially hydrolyzedcellulose ester, such as cellulose acetate and copolymers of polyvinylalcohol. The sensitizers are suitable 017 the well known types of silverchloride, silver bromide and silver iodide emulsions and emulsionscontaining mixtures of these halides, containing the usual emulsionaddenda such as antifoggants, spreading agents, coupler compounds, etc.Such emulsions are suitable to use in forming single as well asmultilayer film useful in color photography which customarily include ona support two or more emulsion layers sensitized to different regions ofthe visible spectrum and may or may not contain coupler compounds.According to our invention such color films carry at least one emulsionlayer containing the mentioned combination of sensitizing agents.

.Our invention having been described, we would have it understood thatthe preceding description is by way of example only and that ourinvention is to be taken as limited only by the scope of the appendedclaim.

What We claim is:

A light-sensitive photographic emulsion comprising silver halidesensitized with a sulfur sensitizing agent, a gold salt sensitizingagent and bis-(Y-diethylaminopropyl) disulfide.

